Freshwater converting to

[reefnoob019]

So I have a 55 Gallon Long Aquarium that Im looking to convert into a Saltwater tank over the years. I have a 250 Watt Heater, A Marineland 3500 biowheel filter (350 gallons per hr) and a Top Fin (300 gallons per hr) that cycles the tanks right now, I have a standard flourescent light fixture on there.

I would like to create a sump to help control everything that goes into the saltwater tank and to control the water level, but i have no idea where to start in building the sump lol

Any ideas on where to start/what to begin on? Any information would be great im a noob!